To a solution of 1-t-butoxycarbonyl-4-hydroxypiperidine (2.6 g), dimethyl 2-hydroxy-5-nitroisophthalate (1.6 g) and triphenylphosphine (4.4 g) in a mixture of dichloromethane (40 ml) and tetrahydrofuran (20 ml) was added diethyl azodicarboxylate (2.6 ml) and the mixture was stirred at room temperature for 4 hours. The reaction mixture was concentrated in vacuo. The residue was purified by chromatography on a silica gel column using dichloromethane/ethyl acetate=19/1 as an eluant to afford a yellow solid. To the solid was added hexane/ethyl acetate=4/1 and then the mixture was filtered to give the desired compound (2.2 g, yield 78%) as a white solid.
